Referring to FIG. 1, a conventional electric heating shrink oven has a pre-shrink oven A10 which has an electric heater A11 located at an upper end. When bottles A20 carried by a conveyer belt pass through the pre-shrink oven A10 heated air generated by the electric heater A11 is discharged through air outlets at two inner sides of the pre-shrink oven A10 to position a label A22 previously coupled on a bottle body A21 of each bottle. Such a process has problems in practice, notably:
1. There is a distance between the air outlets of the electric heater A11 at the two inner sides of the pre-shrink oven A10 and the bottles A20. The distance is not adjustable in response to various sizes of the bottles A20 to allow the heated air generated by the electric heater A11 to shrink the label A22 coupled on the bottle body A21.
2. As there is a distance between the air outlets of the electric heater A11 at the two inner sides of the pre-shrink oven A10 and the bottles A20 carried by the conveyer belt, the label A22 cannot be evenly heated and pre-shrunk and positioned on the bottle body A21. Positioning operation of the bottles A20 in the follow-on shrinking process cannot be effectively performed as desired, referring to FIG. 2.